Warning: Just a single 18650 cell has the potential to start a fire in your home / workplace. Building a battery is a very dangerous task that should only be done by an expert in electricity and electronics.

I made this thread in order to leave things crystal clear for the future.
I will update the head post with all the info required, asked, debated, requested in any other ES place.

I start with a small piece of info data I calculated as exactly as I could as deep research, I added to the data my own heat test about the max Amps that pure nickel and nickel plated steel strips stand in the right conductivity range.

Copper, nickel and steel amperage table (insulated)

The table take into account each material own resistivity, heat dissipation properties, average length for 18650 uses, ambience of work (insulated, in groups, in contact with heat generators) and measurements.

As the amount of heat released from a conductor is proportional to the square of the current (resistive heating--> Heat = amperes^2 * electrical resistance) the heat starts to increase exponentially. Beyond poor / bad values you could have melted insulators in high exterior temperatures / poor battery cooling, given the risk it suppose.

Below the optimal values the nickel stays mild and close to ambience temperature, so the efficiency is optimal under those current levels and you can measure with precision the heat generated exclusively by the cells.

Cu, Ni, Steel efficiency chart.png (43.32 KiB) Viewed 58000 times

As nickel and nickel plated steel are extremely difficult to difference at sight, there are an easy homemade test that could be done in order to check if you have one or another.
Take a strip sample and polish / scratch with a dremel tool or simply with a knife on a small area, and put into salty water for 12h to 24h. This is how it looks.
The upper samples are pure nickel ones, and the bottom ones are nickel plated steel. The corrosion is clearly shown. This doesn't discard the steel for welding purposes, if the strips are in good condition would be enough for batteries that will be used in dry environments.

With all new cells and a little care no BMS is required for li-ion 18650.

There are DIY spot welder on E-S easy to do in a few hours for <$30 with car battery.

Thank you for the appreciations, I will add that to my signature

The table is as good as I could made with deep researching of the latest data. I'm completely agree that the length make a difference, the data counts that the length is very similar on the builds, between 8mm and 30mm are the very most of the nickel conductors lenght in 18650 packs.

All the Steel alloys known has between 10x (for carbon steel) to 20x more electrical resistivity than copper. The steel used in nickel tinned steel strips use to be carbon steel with a very thin tin (40 micrometers it is the common) so that is counted together with Amps / heat tests I made between pure nickel and steel for the same section size.

With all new cells and a little care no BMS is required for li-ion 18650.

There are DIY spot welder on E-S easy to do in a few hours for <$30 with car battery.

Thank you for the appreciations, I will add that to my signature

The table is as good as I could made with deep researching of the latest data. I'm completely agree that the length make a difference, the data counts that the length is very similar on the builds, between 8mm and 30mm are the very most of the nickel conductors lenght in 18650 packs.

All the Steel alloys known has between 10x (for carbon steel) to 20x more electrical resistivity than copper. The steel used in nickel tinned steel strips use to be carbon steel with a very thin tin (40 micrometers it is the common) so that is counted together with Amps / heat tests I made between pure nickel and steel for the same section size.

Hey nobuo, what parameters were you using to determine the current carrying capacity for the strips, I mean what is the limiting factor?
I tested a strip of NPS aprox 60x7x0.15mm at 4amps with no perceptible heat build up. This was in open air not insulated at all. I think it could have had a 1-2 more before getting even slightly warm.
This is a great thread you started
Cheers

All the values on the table are the maximum amps before the nickel starts to saturate and getting warm.
The table take into account each material own resistivity, heat dissipation properties, average length for 18650 uses, and measurements.

As the amount of heat released from a conductor is proportional to the square of the current (resistive heating--> Heat = amperes^2 * electrical resistance) the heat starts to increase exponentially. So beyond those values is when the nickel increases the heat noticeably for any small current increase.

Below the values the nickel stays mild and close to ambience temperature, so the efficiency is optimal under those current values and you can measure with precision the heat generated exclusively by the cells.

remember that when the nickel is in real use, although is not really insulated, it works inside an insulating wrapping, this is also taken into account

Thank You, I hope we can make this greater, useful and precise for your future projects.

Just FYI, I've bought some enormous PVC battery shrink wrap in the US from these guys in Northern California. They have a nice formula for converting from battery pack circumference to the shrink wrap width, and they sell by the foot, which is nice. I've bought their 12.2" width shrink wrap.

I think you owe it to the thread to add a do it yourself 800 watt second capacitor dischage available from Fritz right here, http://frikkieg.blogspot.com I made one for about $600 ready to start welding. This is a over 10,000 amp Dual pulse capacitor discharge welder that is voltage adjustable to 23.2 volts and has separate fully adjustable first and second pulses for the ultimate in versatility. To buy a Sunstone CD welder That is only 200 watt seconds will cost $3875 from Power Stream http://www.powerstream.com/spot-welder.htm

riba2233 wrote:I think it's an overkill and waste of money if you are only going to weld 18650 cells. It's 600$ (with electrodes?) and you still have to invest your time by assembling it? And it's way to powerful.

Seeing how the title states "Ultimate Repository" you think you would have the ultimate hobby spot welder listed and not just a battery short circuit device. As far as a waste of money the same could be said about yours since it's only good for one thing while this one will work with anything now or coming in the future of this EVER changing battery world and weld any material I want to attach. When in the hell would anyone on this site be upset with "too powerful?" That is never used in a sentence on this forum!!! As far as price yours will cost $350 U.S. With 2 batteries and a power supply and then you still need to buy a battery charger for the car batteries. Some people don't mind paying for and/or building a high quality tool that will last for many years through the evolutions of things to come and not just get by with a toy by comparison.

litespeed wrote:
Seeing how the title states "Ultimate Repository" you think you would have the ultimate hobby spot welder listed and not just a battery short circuit device. As far as a waste of money the same could be said about yours since it's only good for one thing while this one will work with anything now or coming in the future of this EVER changing battery world and weld any material I want to attach. When in the hell would anyone on this site be upset with "too powerful?" That is never used in a sentence on this forum!!! As far as price yours will cost $350 U.S. With 2 batteries and a power supply and then you still need to buy a battery charger for the car batteries. Some people don't mind paying for and/or building a high quality tool that will last for many years through the evolutions of things to come and not just get by with a toy by comparison.

I'm not saying yours isn't adequate.......it's just not the ultimate!

Tom

There's no need for tone like that. I just made a few points and asked a few questions, but guess you got a bit to upset to answer them, and just started bashing.
Please don't lie, my welder wont cost 350$. And while it might be "just battery short circuit device" (LOL), what is yours, capacitor short circuit device? What do you think, which one has nicer pulse shape and more controllable pulse?

So, my point was that this is ultimate 18650 spot welding repository, and your welder is total overkill for 18650 cells. That's because you can't weld material that is too thick for 18650 cell, because you will destroy them. So, if you want to weld 18650 cells (not some thick sheet metal), your welder is too expensive, and demands labor and skills. Especially for someone who just wants to make a pack for himself.
I also didn't mention my spot welder, let alone compare it to yours, because they are whole different leagues.

So, ease up on your tone, and contribute to the topic by answering questions you have been asked. Bashing someone with lies and ad hominem is not the right way to contribute on forum. Thanks.